This invention relates generally to the field of fluid flow and, more specifically, to a flow regulating control valve and method for regulating fluid flow.
Fluid valves are used extensively in industry for many applications. An example is the use of fluid valves in heat exchanging systems in buildings for heating or cooling purposes. In many applications, it is often desirable to maintain a constant flow rate through a fluid valve despite fluctuations that may occur in the pressure of the upstream or downstream fluid. It is also desirable in some instances to be able to adjust the flow rate through a valve.
Some prior valves achieve a constant flow by attempting to maintain a constant differential pressure across a control orifice by allowing the differential pressure to act on a piston opposed by an elastic member of nearly constant force. The motion of said piston controls the size of a throttling restriction, which is placed downstream of the control orifice. A consequence of this is that an edge of the piston adjacent the throttling restriction is acted upon by the downstream pressure, which is lower than either of the pressures affecting the intended regulation. This lower pressure tends to cause the throttling restriction to close further than it should for proper regulation, resulting in a lower flow than intended. The dynamic forces arising from the flow of the fluid tend to further lower the pressure acting on the throttling restriction due to Bernoulli""s principle. The error becomes greater as the total pressure differential across the device increases. This phenomenon is referred to as xe2x80x9csagxe2x80x9d and various attempts have been made to limit its effect. Such previous attempts, however, have worked correctly only for a particular flow rate, as is the case of the special pattern of openings disclosed in U.S. Pat. No. 4,080,993 entitled In-Line Flow-Control Valve, to Charles F. Lind.
According to one aspect of the invention, a fluid regulating control valve includes a housing having an upstream region and a downstream region and having a control orifice formed therein adjacent the downstream region and a piston slidably disposed within the housing. The piston has a fluid passage defining an intermediate region disposed between the upstream region and the downstream region and an edge adjacent the upstream region. The valve also includes an elastic member disposed within the housing for opposing translation of the piston within the housing and a throttling element adjacent the upstream region. The throttling element has a throttling surface adjacent the edge of the piston, in which the throttling surface and the edge define a throttling orifice therebetween. The valve further includes an equalization aperture formed in the housing to allow a fluid in the downstream region to enter an equalization chamber defined by a region between an inside surface of the housing and an outside surface of the piston.
According to another aspect of the invention, a fluid regulating control valve for controlling a flow of a fluid includes a housing having an upstream region, a downstream region, and an intermediate region disposed between the upstream region and the downstream region. The valve is formed with a throttling orifice disposed between the upstream region and the intermediate region. The throttling orifice is adapted to dynamically change in size in response to a change in a pressure of the fluid in the upstream region. The valve is also formed with a control orifice disposed between the intermediate region and the downstream region. The control orifice is set to a predetermined size to regulate a flow rate of the fluid.
Embodiments of the invention provide a number of technical advantages. Embodiments of the invention may include all, some, or none of these advantages. For example, one embodiment of the invention allows improved flow regulation over a wide range of flows for a single device by placing a throttling element upstream of a control orifice and balancing the dynamic forces arising from the flow against the forces arising from the higher pressure. By throttling against a pressure which is higher, rather than lower, than the intermediate pressure, the device has a tendency to be disturbed to a more open position, rather than a more closed position. This tendency may then be balanced by the pressure reductions resulting from the fluid velocity to achieve a constant flow rate. By achieving this balance, the throttling edge is not required to be thin, as was the case with many prior devices. Avoiding this thin edge improves the durability and manufacturability of the device.
The present invention also reduces the risk of cavitation. This is because the larger pressure drop across the throttling portion occurs before the smaller pressure drop across the control orifice.
Other technical advantages are readily apparent to one skilled in the art from the following figures, descriptions, and claims.